High dielectric material and method of making same



Patented Apr. 23, 1946 man pmanc'mrc MATERIAL AND METHOD or mxmo sans Eugene Wainer, Niagara Falls, N. Y., assignor to The Titanium Alloy Manufacturing Company, New York, N. Y., a corporation of Maine No Drawing. Original application June 11, 1943,

Divided and this application June 21, 1944, Serial No. 541,474

Serial No. 490,485.

40laims.

The present invention relates to ceramic dielectric materials and to methods of making the same, More particularly, the invention relates to such materials in which compounds of titania as the predominating constituent are used in combination with compounds or tin,

This is a division of Serial No. 490,485, filed June 11, 1943. In copending applications for patent, Ser. No. 465,387, filed November 12, 1942, and Ser. No. 482,613, filed April 10, 1943, the useful properties of barium titanate-strontium titanate mixtures are described. The present invention relates to another group of bodies whose usefulness is equally widespread, in that this group of ceramic compositions has properties such as to make them useful as capacitors in radio, television and communications generally, as capacitative temperature compensating devices in receivers and communication equipment to prevent distortions due to changes in circuit characteristics caused by temperature changes. The dielectric constants of some of these compositions are so high that their utilization in low frequency distribution and communication systems such as 60 cycle lines, by means of. capacitative coupling between a low frequency (20 to 120 cycle) high tension transmission line and communication telephone line, is made possible.

Further, the very high dielectric constants of the ceramic composition of the present invention my novel compositions have possible utility inplezoelectricity, Supersonics, crystal or condenser microphones, frequency stabilizers, loud speakers, phonograph pick ups, telephone design, and

oscillator designs generally. The foregoing remarks apply particularly to those bodies whose dielectric constants are over 1000 at radio frequency. In condenser microphones, very thin sheets of the higher dielectric constant materials are rigidly clamped at either the center or edges and used as vthe vibrating diaphragm. The minute changes of positionor dimension of the dielectric due to vibration will occasion relatively large changes in capacity by means of which sound is transformed into electrical energy.

Other members of this group, particularly those having dielectric constants over 1000 exhibit electrical and mechanical characteristics of the same nature as piezo electrical and pyroelectrical crystals. For example, a rod of the material having one end fixed and one end free to vibrate will when in vibration, develop a potential difference of several volts between the two ends of the rod.

The particular usefulness of members of this group as compensators for correction of frequency drift, lies not only in the possibility of obtention of both positive and negative temperature coefllcients of a wide variety, but also the possibility of controlling the degree of variation through choice of the proper composition. These properties, coupled with extremely low power factors in some cases, ail'ord a high degree of usefulness for this latter class of application.

In general, the novel compositions of the present invention comprise fired mixtures of the titanates and stannates of the alkaline earth metals, In a broad sense these mixtures may consist of one or more titanates with one or more stannates. While the alkaline earth metal compounds generally are of utility in the present invention, those of particular importance are the stannates and titanates of barium, strontium and calcium. In general the total stannate content of the ceramic body will not exceed 50%. The'generai classes of compositions covered by this invention are indicated in the examples. The peculiarly beneficial effect of the stannate additions is most strikingly shown in the case of such additions to barium titanate. barium titanate has a dielectric constant of 1200-1300, and a temperatureccoemcient which is first negative, then strongly positive, and finally strongly negative between 20 C. and C. Not only may this erratic behavior be eliminated by addition of the stannates but dielectric constants at least as high as 13,000 at radio frequencies are possible.

In the practice of the invention the ingredients as indicated in the table below are properly reacted ceramically and then ground so that the coarsest particles will pass a 325 mesh screen. The dried powders are then mixed within the limits indicated by the proportions given in the table. Approximately 10% water is added and thoroughly mixed in and the damp powder granulated by passage through a 20 mesh screen. The granules are then pressed in a die under a pressure of 5 to 10 tons per square inch, and

then allowed to air dry for 24 hours. The pieces used for purposes of test were roughly 1 inch in diameter and 0.1 inch thick. Pieces of such size were fired on a schedule of 400 F. per hour to the peak temperature, then held at peak temperature for three hours and then allowed to cool. The maturation temperature for all the bodies listed below is between 2450 and 2500 F. After cooling the opposing parallel surfaces are painted At radio frequencies vanometer. The 1000 cycl measurements were obtained through use of an impedance bridge of standard design, whose arms were resistive components.

Having described the method of practice or the invention, the following sets of tables indicate the type of compositions and the values obtained thereon.

The peculiar advantage of such compositions as capacitor materials for by-pass and filter condensers may be seen from perusal of the following figures. For example, present day electrolytic condensers at best have power factors between 6.0% and 16.0% whereas all the values in the table are below 3.0%. Thus such materials may be used as substitutes for paper and electrolytics. Bodies having power factors below 0.1% are suitable as substitutes for mica capacitors. The possibility of variation and control of temperature coeiflcients, thus making available these compositions as compensator compositions, is indicated from the data given in Table V and following. These temperature coefficients were measured at one megacycle.

Table I.--CaTiOa series One megacycle One kilocycle Comp.

No. Ca'lnO; stannate Dielec F g DMec F g) ac r, no r, percent percent 100-P11385110: 162 0.010 171 1. 3 100+5BBSnOz..- 158 0.010 165 1.3 100+10B&SnO3 148 0. 010 161 1.3 80+20B11SH03..- 131 0. 010 139 1. 2 65+35BBS1J 142 0.015 149 1. 3 50+5OBBSI103 133 0.015 140 1. 4 100+1SrSnOa. 145 0.010 155 1.4 100+5SrSnO: 133 0. 010 148 1. 4 100+10SrSnOa 132 0. 010 137 1. 4 80+20SrSnOa 107 0. 010 123 1. 4 65+35SrSnO 77 0. 010 86 1. 7 O+5OSrSl1O3 57 0.030 78 2. 5 100+1C8Stl0a. 150 0. 010 157 1. 4 100+5C8S1103 145 0. 010 153 1.3 IOO-HOCaSnOa 132 0. 010 142 1. 4 8O+20CBS11O3 103 0. 010 117 1. 4 65+35CBSI103 76 0. 010 85 2. 1 50+50C8Sl10a 61 0.010 72 1.8

Table II .SrTzO3 senes One megacycle One kilocycle Comp. v

No. Sr'l x0; stannate Dielec Pow Dielee Power mn fan i factor nlmxll f actor percen L percent IOO-HBRSIJO; 249 0. 010 260 1. 1 100+5BaSnOa. 247 0. 010 240 1. 0 l00+l0BaSnO= 210 0. 010 22) 1. 7 804-2113238110 233 0. 010 237 1. 2 (SH-3513215110 155 0.040 163 1. 9 50+50BaSn03 99 0. 030 97 1. 6 100+1SrSnOa... 242 0.040 244 1. 2 100+.' SrSn0; 227 0.060 238 l. 2 215 0. 080 217 1. 2 144 0. 010 149 1. 7 76 0. 010 84 2. 0 45 0. 030 52 B. 0

208 0. 020 214 l. 1 804-2101331101 141 0. 010 146 1. 3 (NH-35085110: 97 0. 010 113 2. 6 50+50CaSn0; 75 0. 010 85 1. 6

Table [IL-B11110; series One megacycle One kilocyclo BaTlO rstannate Dielec. Dielec. 'f percent percent NIH-13351101. 1, 525 0.82) 1, 590 1. 0 NIH-513581101- 2, 010 1.190 2,155 1. 6 100-{4013581101 3, 5&1 2. no 3, 970 1. 4 UH-NBBSXIO 4, 175 0. 870 4, 275 0. 01 664-3161338110 679 0. 420 683 0. 03 50+50Ba8n0 203 0x0 280 2.8 1m+1BrBnO;. 1, 650 0. 950 1, 730 1. 1 lfliH-bsrsnol 2, 3(1) 1. 5(1) 2, 470 1. 8 100140313110: 4, am 0. 9&1 4, 7H) 2. 4 80+fi18r5n0g... 1, 720 0. 31) 1, 735 0. 01 +35Sr8n0; 593 0. 230 605 0. 06

505131101." 272 0.1K) 276 1. 6 100+1C8SI10:.. 1,710 1.100 1,790 1.4 IOO-I-BCBEBOL 2, 080 2. M) 2, 840 1. 8 100+10Ca5n0r- 8, 5(1) 2. 5(1) 9, 400 1. 5 +Z1Ca8110n-.. 1,42) 0.320 1,445 0.02 65+350a5n0z 235 0. 000 238 1.1 504-5001151101 124 0. 010 130 1. 4 92+8Ba8n0; 2, 810 2. 62) 3,290 2. 0 88+12BaSn0; 6, 575 2. 720 7, 060 1. 2 86+14BaSn03 9, 450 2. 9(1) 10, 210 0. 8 84+16 BaSnO; 12, 600 2. 200 13,100 0. 4 82+18BBSI10: 7, 550 1. 090 7, 250 0.1

Table I V.-Comple:c 8T288 One megacycle One kilocycle Comp.

Composition Dielec P Dielec 22" no or, no r, mm percent constant percent 1 SOBaTiOz IOBaSnO; 4,160 0. 95 3, 510 0. 01

l0SrSn(5;. 2 7013211101, 2013738110, 1, 460 0. 38 1, 415 0. 01

l0SrSnO;. 3 7013011101, 101388110 2,105 0.50 1, 805 0. 02

mSrSnOn 70Ba110a IBBaSnOg, 1, 475 0.31 1, 450 0.10

ISSrSnd 85Ba1i0r, 53881103, 7, 720 1. 74 8, 0 60 5SrSn 5StIiOz. 70BaTiO: 101355110 1, 350 0. 23 1, 320 0. m

IOSISnda, IOSlTlOz. 7 65 Ba'IiOz, 15 BaSnOz, 615 0.16 625 1. 30

15SrSnOa, 15SrTiOz.

Table V.--Temperature capacity data Body #3, Body #9, Body #15, 0:51:10; CaTiO; CaTiOi Temperature, C. series series series K K K Table VI .--Temperature capacity data Body #3, Body #9, Body ll5,

BlTiO: SrTlOz SrTlO: Tempera ure, C. series series series 210 215 208 210 215 208 $18 215 207 207 213 $16 205 212 115 203 210 203 201 KB 202 198 K16 199 196 206 197 .193 Z14 194 189 202 191 186 200 188 184 198 184 190 182 Table lift-Temperature capacity series Body #3, Body #9, Body #15, Body #5, g'a na'rioi na'rioi aa'rioi complex series K series K series K series K The temperature coeilicients oi the compositions covered in Tables V, VI and VII are indicative oi the scope of variation possible. While single compositions may yield the desired coefllcient, an

infinite variety of coemcient is possible through parallel combination of one or more bodies.

From the foregoing it will be seen that the presnt invention provides compositions eminently suitable as dielectric materials in a wide variety of uses. The above examples have been set forth as illustrative of the invention, the scope thereof being comprehended within the appended claims as it will be apparent that wide variation may be had from the specific examples.

What is claimed is:

l. A ceramic composition which comprises strontium titanate and an alkaline earth stannate.

2. A ceramic composition which comprises strontium titanate and calcium stannate.

3. A ceramic composition which comprises strontium titanate and strontium stannate.

4. A ceramic compostion which comprises strontium titanate and barium stannate.

EUGENE WAINER. 

